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I plan to build a small garage, 20 feet by 30 feet. I want to be able
to span the 20 foot width, so that I don't have to use interior posts.

At first, I was doubtful this could be done, and I have seen comments in
these groups that this is not really feasible. Yet, I have closely
inspected one of the yard sheds (with loft) at Home Depot, that is 16 feet
wide, using 2 x 10 beams on 12 inch centers. It is a yard shed, with a
small loft. I went up into the loft area to see what "bounce" the floor
had, and it is quite solid, with just a small hint of a bounce (I weigh
215 lbs). So, I have concluded that spanning 16 feet with 2 X 10's
is easy, as I have seen it.

But, I know that going from 16 ft to 20 ft wide is 4 feet more of
span and is 25 % more of a span. I am a novice, but I try to find
answers for myself first. Somehow, I got a span table for Southern Pine
lumber. The title of the chart is

I plan to use the loft only for very light storage, but these "load"
figures seem very low to me. But, once again, I have "felt" what a 16
ft span using 2 x 10's feels like, and it seems very sturdy to me.

From the chart, it appears that a # 2 visually graded (is that what you
"usually" find in lumber yards and the big box stores??) 2 X 10
beam on 12 inch centers will span 19 ft, 11 inches.

A 2 x 12 beam on 16 inch centers will span 20 ft, 2
inches.

-----------------------

Questions: First, am I on the right track ? Does the chart seem to apply
to my needs and plans? I could email the chart (pdf format) to anyone who
wanted to look, I don't think I should post an attachment here on a news
group.

Is #2 visually graded, the most common lumber found in lumber yards ?

Which would be better, 2 x 10 on 12 inch centers or 2 x 12 on
16 inch centers ?? It seems that the latter may be a bit cheaper, but price
isn't the primary concern.

What happens if you use a 2 X 12 beam, but put them on 24 inch centers
instead of 16 inch?? Do you simply get more deflection, and less load
capacity ?

2 x 10 spanning 20 foot will sag under their own weight. 2 x 12
would work if the load is really light. You want nothing in the
way of parking. That is reasonable but would it be possible to
have a drop from the ridge every 4 feet with a stiffback? 2 x 8's
would work that way quite well. Even push the envelope with
proper dropping braces using 2 x 6's as that's only a 10 foot span
less the cantilevering effect in the center of continuous joists.
Certainly, the latter would hold a bigger load than the 2 x 12's..

Example: I have a garage that is 24 feet wide. I have no ceiling
in it except 2 x 6 joists (cross ties) every 4 feet. They are
nailed heavily to 2 x 6 rafters on 5 and 12 pitch. I have a 1 x 4
drop nailed onto the rafter at the ridge and dropping down and
nailed onto the joists. To not split the 1'x, I stapled them with
multiple 2-1/2"staples. I have a 6 x 6 - 5 feet long laying
across 2 of them and think nothing of pulling a 8 cylinder engine
on them. I wouldn't even think of doing that even spanning across
four 2 x 12's.

"James" wrote in message
I plan to build a small garage, 20 feet by 30 feet.
I want to be able to span the 20 foot width, so that I
don't have to use interior posts.

At first, I was doubtful this could be done, and I have
seen comments in these groups that this is not really
feasible. Yet, I have closely inspected one of the
yard sheds (with loft) at Home Depot, that is 16 feet
wide, using 2 x 10 beams on 12 inch centers. It is
a yard shed, with a small loft. I went up into the loft
area to see what "bounce" the floor had, and it is quite
solid, with just a small hint of a bounce (I weigh 215
lbs). So, I have concluded that spanning 16 feet with
2 X 10's is easy, as I have seen it.

But, I know that going from 16 ft to 20 ft wide is
4 feet more of span and is 25 % more of a span. I am
a novice, but I try to find answers for myself first.
Somehow, I got a span table for Southern Pine lumber.
The title of the chart is

I plan to use the loft only for very light storage, but
these "load" figures seem very low to me. But, once
again, I have "felt" what a 16 ft span using 2 x
10's feels like, and it seems very sturdy to me.

From the chart, it appears that a # 2 visually graded
(is that what you "usually" find in lumber yards and the
big box stores??) 2 X 10
beam on 12 inch centers will span 19 ft, 11 inches.

A 2 x 12 beam on 16 inch centers will span
20 ft, 2 inches.

-----------------------

Questions: First, am I on the right track ? Does the
chart seem to apply to my needs and plans? I could email
the chart (pdf format) to anyone who wanted to look, I
don't think I should post an attachment here on a news
group.

Is #2 visually graded, the most common lumber found in
lumber yards ?

Which would be better, 2 x 10 on 12 inch centers
or 2 x 12 on 16 inch centers ?? It seems that
the latter may be a bit cheaper, but price isn't the
primary concern.

What happens if you use a 2 X 12 beam, but put them
on 24 inch centers instead of 16 inch?? Do you simply
get more deflection, and less load capacity ?

I plan to use the loft only for very light storage, but these "load"
figures seem very low to me. But, once again, I have "felt" what a 16
ft span using 2 x 10's feels like, and it seems very sturdy to me.

As a theoretical matter, to maximize span for a given floor thickness
the entire floor structure should be designed as an engineered
structure, with sub-flooring, fasteners schedules, adhesives,
dimensional and engineered members, etc. specified together. By
adjusting these variables a structural engineer can spec designs for
residential floor spans of 3O'+ using readily available components.

As *practical matter*, my first question would be: "What does the
local building department require?". Your question may be answered
right there, and there might be some surprises - for example since you
now have a load bearing second floor, you may find substantial footings
are required below the exterior walls.

My second question, if you are permitted to build as you please, would
be "What is a reasonable design criteria considering the loads that
might reasonably be placed on the floor by subsequent owners?"-
keeping in mind that they may stack old newspapers up there...

Once you know those numbers (load sq/ft and allowable deflection), as
specified by local code or derived by common sense, you are ready to
start thinking about materials and techniques.

You will need to have it engineered and they will tell you what you
need to do. In order to get a permit you will need plans and the plans
will need tom have an engineers stamp on them! If it is not required
you should still get it done or at least approved by a PE.

That said on This old house they had a span they needed to raise the
ceiling on. They cut the joists from 12 to 10" and bolted steel plate
cut to size they also had sag and used the edge of the steel to judge
when the floor was level using floor jacks to jack the ceiling. I
would think with the steel plates on both sides of 2x12's you should be
fine. But the snow load will also have an effect as well as the roof
pitch!
I had a barn built with a 60' clear span. it had 2 with beams bolted
together.

I plan to build a small garage, 20 feet by 30 feet. I want to be
able to span the 20 foot width, so that I don't have to use interior
posts.

At first, I was doubtful this could be done, and I have seen comments
in these groups that this is not really feasible. Yet, I have
closely inspected one of the yard sheds (with loft) at Home Depot,
that is 16 feet wide, using 2 x 10 beams on 12 inch centers.
It is a yard shed, with a small loft. I went up into the loft area
to see what "bounce" the floor had, and it is quite solid, with just
a small hint of a bounce (I weigh 215 lbs). So, I have concluded
that spanning 16 feet with 2 X 10's is easy, as I have seen it.

But, I know that going from 16 ft to 20 ft wide is 4 feet more
of span and is 25 % more of a span. I am a novice, but I try to
find answers for myself first. Somehow, I got a span table for
Southern Pine lumber. The title of the chart is

I plan to use the loft only for very light storage, but these "load"
figures seem very low to me. But, once again, I have "felt" what a
16 ft span using 2 x 10's feels like, and it seems very sturdy
to me.

From the chart, it appears that a # 2 visually graded (is that
what you "usually" find in lumber yards and the big box stores??)
2 X 10 beam on 12 inch centers will span 19 ft, 11 inches.

A 2 x 12 beam on 16 inch centers will span 20 ft, 2
inches.

-----------------------

Questions: First, am I on the right track ? Does the chart seem
to apply to my needs and plans? I could email the chart (pdf
format) to anyone who wanted to look, I don't think I should post an
attachment here on a news group.

Is #2 visually graded, the most common lumber found in lumber yards ?

Which would be better, 2 x 10 on 12 inch centers or 2 x
12 on 16 inch centers ?? It seems that the latter may be a bit
cheaper, but price isn't the primary concern.

What happens if you use a 2 X 12 beam, but put them on 24 inch
centers instead of 16 inch?? Do you simply get more deflection, and
less load capacity ?

have you considered wood i joists? bring your plan to a lumberyard and
they will do the design for you. or google "truss joist macmillan" for
example to find simple span tables) i joists are easier to install
(lighter), straighter, and can span longer spans. comparably priced to
sawn lumber.

James wrote:
This place is so remote, they have never heard of a building inspector.

Then build anything you want and watch and see if it collapses. However, I
don't know of any place in the western world where building codes don't apply.
BTW - your insurance agent may have something to say about this, too.
And yes, I will have 36 inch depth, 12 inch wide poured footings around
the perimeter of the garage.

Which means nothing without knowing what the soil is like.

BTW 2x10 would not be legal for that kind of span as a _floor_ where I live.
Without checking, I don't think 2x12 would work either - 2x14 sounds about right.

James wrote:
This place is so remote, they have never heard of a building inspector.
And yes, I will have 36 inch depth, 12 inch wide poured footings around
the perimeter of the garage.

Sounds like you are headed in the right direction: thinking of this as
a serious structure, not just an up-sized "garage" on a pad + loft
space. I'm not an engineer, and I try hard not to play one the net, but
I *do* know that some of the scariest things I've seen in new
construction in my area result from architects and/or builders who land
jobs to build 'McMansons" and just assume that the materials and
techniques that worked for a living room with a 22' clear span can be
"up-sized" to work at 26' even 30 or even 35' - there is a 4M
dollar house not too far from me where the second contractor on the
project worked with an engineering firm for six months to stabilize
such a structure, essentially erecting a permanent structural steel
frame inside the existing footprint to literally keep the building from
collapsing.